使用stoplight示例对调用的方法进行java澄清

Question

下面的代码出现在我的书中关于方法的章节中。有几件事我有点困惑

1. 当我相信run()方法正在调用createFilledCircle方法时，我的理解正确吗
2. run()方法是接收者，而createFilledCircle方法是发送者吗
3. 对于三个add(createFilledCircles...red,yellow and green);程序员如何知道参数中允许哪些信息？在add(createFilledCircle)中是否使用了(x location, y location, width of figure, height of figure)的格式

import acm.program.*;
import acm.graphics.*;
import java.awt.*;

public class StopLight extends ConsoleProgram {
  public void run() {
    double cy = getWidth() / 2 ;
    double cx=  getHeight() / 2; 

    double fx = cx - (FRAME_WIDTH / 2);
    double fy = cy - (FRAME_HEIGHT /2 );

    double dy = (FRAME_HEIGHT / 4 ) + (LAMP_RADIUS / 2);

    GRect frame = new GRect (fx, fy, FRAME_WIDTH, FRAME_HEIGHT);
    frame.setFilled(trye);
    frame.setColor(Color.GRAY);
    add(frame);

    add(createFilledCircle(cx, cy-dy, LAMP_RADIUS, Color.RED));
    add(createFilledCircle(cx, cy, LAMP_RADIUS, Color.YELLOW));
    add(createFilledCircle(cx, cy + dy, LAMP_RADIUS, Color.GREEN));
  }

  private GOval createFilledCircle (double x, double y, double r, Color color) {
    GOval circle = new GOval (x -r, y -r, 2 * r, 2 * y );
    circle.setFilled(true);
    circle.setColor(color);
    return circle; 
  }

  private static final double FRAME_WIDTH = 50; 
  private static final double FRAME_HEIGHT = 100;
  private static final LAMP_RADIUS = 10; 
}

Answer 1

1) Is my understanding correct when I believe that the run() method is calling the createFilledCircle method?

对

2) Is the run() method the receiver and the createFilledCircle the sender?

我不知道你说的“接收者”和“发送者”是什么意思。这些不是人们在谈论被调用的方法时通常使用的术语

（它看起来像是Smalltalk编程语言中的术语，Smalltalk编程语言是一种早期的面向对象语言。鉴于此，它正好相反：你会说run是发送方createFilledCircle是接收方。）

3) for the three add(createFilledCircles...red,yellow and green); how does the programmer know what information is permitted in the argument? Is the format of (x location, y location, width of figure, height of figure) being used in the add(createFilledCircle)?

createFilledCircle方法的声明指定了该方法需要的参数：三个double值和一个Color值

在这样一行中：

add(createFilledCircle(cx, cy-dy, LAMP_RADIUS, Color.RED));

发生的情况是，首先使用参数cx, cy-dy, LAMP_RADIUS, Color.RED调用createFilledCircle，然后将方法createFilledCircle的返回值（即GOval值）传递给add方法。与此相同：

GOval result = createFilledCircle(cx, cy-dy, LAMP_RADIUS, Color.RED);
add(result);

Answer 2

1）是的——它在

add(createFilledCircle(cx, cy-dy, LAMP_RADIUS, Color.RED));
  add(createFilledCircle(cx, cy, LAMP_RADIUS, Color.YELLOW));
  add(createFilledCircle(cx, cy + dy, LAMP_RADIUS, Color.GREEN));

2）它是发送方，但add（）方法是接收方

3）createFilledCircle已使用

createFilledCircle (double x, double y, double r, Color color)